1. Field
Exemplary embodiments of the present invention relate to a data transmission circuit and a semiconductor memory device having the same.
2. Description of the Related Art
In general, as the process technology of semiconductor memory devices including a Double Date Rate Synchronous DRAM (DDR SDRAM) is gradually advanced, the number of memory banks provided in a semiconductor memory device has gradually increased. In order to efficiently input and output data to and from the memory banks, the design technology of semiconductor memory devices has been developed in various manners. For example, the design technology may include a method for arranging a plurality of memory banks in a stack structure, or a method for changing an interface between a controller and a semiconductor memory device according to various operation modes such as X4 and X8.
The above-described operation modes such as X4 and X8 for increasing the diversity of interfaces in the semiconductor memory device may relate to operation modes for adjusting the number of data input/output pads (typically, referred to as DQ pads) which are used when data are transferred between the controller and the semiconductor memory device. For example, in the case of a semiconductor memory device including eight data input/output pads, the operation mode thereof may be set to X8 or X4. When the operation mode of the semiconductor memory device is set to X8, the semiconductor memory device performs a data input/output operation through eight input/output pads. When the operation mode of the semiconductor memory device is set to X4, the semiconductor memory device performs a data input/output operation through four data input/output pads.
Meanwhile, when an operation of inputting data to a semiconductor memory device (write operation) is performed, the data is inputted through a data input/output pad from the outside of the semiconductor memory device. Then, the inputted data is transmitted to a write driver through a global line. The write driver transfers the data to a local line. The data of the local line is transmitted to a bit line through a bit line sense amplifier selected by an address and then stored in a memory cell.
When an operation of outputting data of the semiconductor memory device (read operation) is performed, data of a memory cell is transmitted to a bit line. The data of the bit line is amplified by a bit line sense amplifier and transmitted to a local line. The data of the local line is amplified by a main amplifier and transmitted to a global line. The data of the global line is transmitted to the outside of the semiconductor memory device through a data input/output pad.
Here, the numbers of local lines and global lines which are actually used for data input/output operations may differ according to operation modes of the semiconductor memory device, such as X4, X8, and the like. For example, when eight data are inputted (or outputted) per one input/output pad in the X8 operation mode (total 64 data are inputted or outputted), 128 local lines and 64 global lines are used. When eight data are inputted (or outputted) per one input/output pad in the X4 operation mode (total 32 data are inputted or outputted), 64 local lines and 32 global lines are used. Since data transmitted to the local lines are recognized by differential amplifiers, two actual local lines, i.e., one pair of local lines, are used to transmit one data.
The conventional semiconductor memory device transmits 64 data to 128 local lines during a data output operation regardless of whether the operation mode thereof is X8 or X4. Then, depending on the operation modes, the conventional semiconductor memory device operates as follows. In the case of the X8 operation mode, 64 data loaded in 128 local lines are transmitted to 64 global lines through the control of main amplifiers coupled between the local lines and the global lines. Furthermore, in the case of the X4 operation mode, 32 data loaded in 64 local lines are transmitted to 32 global lines, respectively, but 32 data loaded in the other 64 local lines are not transmitted to global lines.
Since the data transmission is performed through a flowing current, the current are passed through the bit lines, the local lines, and the global lines during the data transmission. As the conventional semiconductor memory device transmits the 32 data, which are not to be outputted, to the local lines from a memory bank, unnecessary currents passes through inside of the semiconductor memory device (in particular, when the semiconductor memory device operates in the X4 operation mode). As a result, the power consumption of the semiconductor memory device inevitably increases. Even when the semiconductor memory device performs data input/output operations, similar concerns may occur.